




版權(quán)說明:本文檔由用戶提供并上傳,收益歸屬內(nèi)容提供方,若內(nèi)容存在侵權(quán),請進(jìn)行舉報或認(rèn)領(lǐng)
文檔簡介
WilliamStallings
DataandComputerCommunicationsChapter15LocalAreaNetworkOverview115.1LANApplications(1)PersonalcomputerLANsLowcostLimiteddatarateBackendnetworksInterconnectinglargesystems(mainframesandlargestoragedevices)HighdatarateHighspeedinterfaceDistributedaccessLimiteddistanceLimitednumberofdevices2LANApplications(2)StorageAreaNetworksSeparatenetworkhandlingstorageneedsDetachesstoragetasksfromspecificserversSharedstoragefacilityacrosshigh-speednetworkHarddisks,tapelibraries,CDarraysImprovedclient-serverstorageaccessDirectstoragetostoragecommunicationforbackupHighspeedofficenetworksDesktopimageprocessingHighcapacitylocalstorageBackboneLANsInterconnectlowspeedlocalLANsReliabilityCapacityCost3個人計(jì)算機(jī)局域網(wǎng)客戶/服務(wù)器計(jì)算模式
后端網(wǎng)絡(luò)和存儲區(qū)域網(wǎng)
大型系統(tǒng)互聯(lián):大型機(jī)、海量存儲
特征:高速高可靠性、有限數(shù)量和距離
高速辦公室網(wǎng)絡(luò)
大信息量數(shù)據(jù)處理
骨干局域網(wǎng)高帶寬、高可靠性實(shí)現(xiàn)速率相對較低的LAN的互聯(lián)局域網(wǎng)應(yīng)用5后端網(wǎng)絡(luò)與存儲區(qū)域網(wǎng)(1)大系統(tǒng)的互聯(lián)大型機(jī)(Mainframes)巨型機(jī)(Supercomputers)海量存儲設(shè)備(Massstoragedevices)主要需求小范圍內(nèi)有限數(shù)量的設(shè)備之間的批量數(shù)據(jù)傳送典型特征高數(shù)據(jù)率高速接口分布式接入有限距離有限設(shè)備數(shù)量6后端網(wǎng)絡(luò)與存儲區(qū)域網(wǎng)(2)SAN–網(wǎng)絡(luò)存儲設(shè)備硬盤磁帶庫CD陣列715.2.1TopologiesTreeBusSpecialcaseoftreeOnetrunk,nobranchesRingStar9LANTopologies10BusandTreeTopologyMultipointmediumTransmissionpropagatesthroughoutmediumHeardbyallstationsNeedtoidentifytargetstationEachstationhasuniqueaddressFullduplexconnectionbetweenstationandtapAllowsfortransmissionandreceptionNeedtoregulatetransmission需要規(guī)定傳輸Toavoidcollisions避免信號沖突Toavoidhogging(擾亂)避免信號混淆Datainsmallblocks-framesTerminatorabsorbsframesatendofmedium11RingTopologyRepeatersjoinedbypointtopointlinksinclosedloopReceivedataononelinkandretransmitonanotherLinksunidirectionalStationsattachtorepeatersDatainframesCirculatepastallstationsDestinationrecognizesaddressandcopiesframeFramecirculatesbacktosourcewhereitisremovedMediaaccesscontroldetermineswhenstationcaninsertframe13Frame
Transmission
RingLAN14StarTopologyEachstationconnecteddirectlytocentralnodeUsuallyviatwopointtopointlinksCentralnodecanbroadcastPhysicalstar,logicalbusOnlyonestationcantransmitatatimeCentralnodecanactasframeswitch15BusLAN
TransmissionMedia(1)TwistedpairEarlyLANsusedvoicegradecableDidn’tscaleforfastLANsNotusedinbusLANsnowBasebandcoaxialcableUsesdigitalsignallingOriginalEthernet17BusLAN
TransmissionMedia(2)BroadbandcoaxialcableAsincableTVsystemsAnalogsignalsatradiofrequenciesExpensive,hardtoinstallandmaintainNolongerusedinLANsOpticalfiberExpensivetapsBetteralternativesavailableNotusedinbusLANsAllhardtoworkwithcomparedwithstartopologytwistedpairCoaxialbasebandstillusedbutnotofteninnewinstallations18RingandStarUsageRingVeryhighspeedlinksoverlongdistancesSinglelinkorrepeaterfailuredisablesnetworkStarUsesnaturallayoutofwiringinbuildingBestforshortdistancesHighdataratesforsmallnumberofdevices19MediaAvailable(1)Voicegradeunshieldedtwistedpair(UTP)Cat3CheapWellunderstoodUseexistingtelephonewiringinofficebuildingLowdataratesShieldedtwistedpairandbasebandcoaxialMoreexpensivethanUTPbuthigherdataratesBroadbandcableStillmoreexpensiveandhigherdatarate21MediaAvailable(2)HighperformanceUTPCat5andaboveHighdatarateforsmallnumberofdevicesSwitchedstartopologyforlargeinstallationsOpticalfiberElectromagneticisolationHighcapacitySmallsizeHighcostofcomponentsHighskillneededtoinstallandmaintainPricesarecomingdownasdemandandproductrangeincreases2215.3ProtocolArchitectureLowerlayersofOSImodelIEEE802referencemodelPhysicalLogicallinkcontrol(LLC)Mediaaccesscontrol(MAC)23IEEE802vs.OSI25802Layers–Physical
物理層的功能Encoding/decoding信號的編碼/解碼Pre’amblegeneration/removal前導(dǎo)碼的產(chǎn)生/去除(用于同步)Bittransmission/reception比特傳輸/接收Transmissionmedium傳輸媒體26邏輯鏈路控制LLC的特性兩站之間傳輸鏈路級不需中間交換節(jié)點(diǎn)必須支持多點(diǎn)接入的共享媒體由MAC承擔(dān)了一些鏈路接入的細(xì)節(jié)尋址包括指定源LLC用戶和目的LLC用戶稱為LLC服務(wù)訪問點(diǎn)(LSAP)典型的用戶是高層協(xié)議29LLCServicesBasedonHDLCUnacknowledgedconnectionlessserviceConnectionmodeserviceAcknowledgedconnectionlessservice提供三種服務(wù)不確認(rèn)的無連接服務(wù)(Unacknowledgedconnectionlessservice)連接方式服務(wù)(Connection-modeservice)帶確認(rèn)的無連接服務(wù)(Acknowledgedconnectionlessservice)30LLCProtocolModeledafterHDLCAsynchronousbalancedmodetosupportconnectionmodeLLCservice(type2operation)UnnumberedinformationPDUstosupportunAcknowledgedconnectionlessservice(type1)TwonewunnumberedinformationPDUstosupportAcknowledgedconnectionlessservice(type3)MultiplexingusingLSAPs31LLC協(xié)議以HDLC為藍(lán)本第1類操作無編號信息PDU支持不確認(rèn)的無連接服務(wù)第2類操作異步平衡方式支持連接方式LLC服務(wù)第3類操作兩個新的無編號PDU支持帶確認(rèn)的無連接服務(wù)利用LSAP實(shí)現(xiàn)多路復(fù)用3215.3.3802Layers-
MediaAccessControlAssemblyofdataintoframewithaddressanderrordetectionfieldsDisassemblyofframeAddressrecognitionErrordetectionGovernaccesstotransmissionmediumNotfoundintraditionallayer2datalinkcontrolForthesameLLC,severalMACoptionsmaybeavailable33MAC子層的功能在發(fā)送方,將數(shù)據(jù)配以地址與差錯檢測字段組裝成幀在接收方,拆解幀地址辨識差錯檢測監(jiān)管傳輸媒體的接入在傳統(tǒng)的第二層數(shù)據(jù)鏈路控制中無此功能34分裂數(shù)據(jù)鏈路層的原因
在傳統(tǒng)的數(shù)據(jù)鏈路(DL)層中不具有管理共享訪問媒體的接入所需的邏輯對于相同的LLC,可以提供幾種MAC選項(xiàng)35LANProtocolsinContext36MediaAccessControlWhereCentralGreatercontrolSimpleaccesslogicatstationAvoidsproblemsofco-ordinationSinglepointoffailurePotentialbottleneckDistributedHowSynchronousSpecificcapacitydedicatedtoconnectionAsynchronousInresponsetodemand37媒體接入控制重要參數(shù)Where集中式(Central)更多的控制簡單的站點(diǎn)接入邏輯避免協(xié)商問題單點(diǎn)故障可能形成瓶頸分布式(Distributed)集體完成MAC功能動態(tài)確定哪個站發(fā)送優(yōu)缺點(diǎn)是集中式方案的鏡像How同步–為每個連接指定固有帶寬異步–按需響應(yīng)38AsynchronousSystemsRoundrobinGoodifmanystationshavedatatotransmitoverextendedperiodReservationGoodforstreamtrafficContentionGoodforburstytrafficAllstationscontendfortimeDistributedSimpletoimplementEfficientundermoderateloadTendtocollapseunderheavyload39異步系統(tǒng)循環(huán)(Roundrobin)若許多站都需持續(xù)一段時間發(fā)送數(shù)據(jù)則很有效輪詢:集中式技術(shù)令牌環(huán):分布式控制預(yù)約(Reservation)適用于流式通信量streamtraffic爭用(Contention)適用于突發(fā)通信量burstytraffic所有站爭用占用媒體時間分布式(e.g.CSMA/CD)實(shí)現(xiàn)簡單在負(fù)荷適中時有效在重負(fù)荷時可能會崩潰40MACFrameFormatMAClayerreceivesdatafromLLClayerMACcontrolDestinationMACaddressSourceMACaddressLLCCRCMAClayerdetectserrorsanddiscardsframesLLCoptionallyretransmitsunsuccessfulframes41MAC幀格式MAC層從LLC層接收數(shù)據(jù)MAC幀的字段MAC控制目的站MAC地址源站MAC地址LLCCRC(FCS)MAC層檢測錯誤并丟棄幀LLC可選設(shè)成重傳不成功接收的幀42TypicalFrameFormat43小結(jié)局域網(wǎng)的應(yīng)用拓?fù)浣Y(jié)構(gòu)和傳輸媒體局域網(wǎng)的體系結(jié)構(gòu)IEEE802參考模型媒體接入控制(Mediaaccesscontrol)邏輯鏈路控制(LogicalLinkControl)4415.4Bridges網(wǎng)橋AbilitytoexpandbeyondsingleLANProvideinterconnectiontootherLANs/WANsUseBridgeorrouterBridgeissimplerConnectssimilarLANsIdenticalprotocolsforphysicalandlinklayersMinimalprocessingRoutermoregeneralpurposeInterconnectvariousLANsandWANsseelater45WhyBridge?ReliabilityPerformanceSecurityGeography4615.4.1FunctionsofaBridgeReadallframestransmittedononeLANandacceptthoseaddresstoanystationontheotherLANUsingMACprotocolforsecondLAN,retransmiteachframeDothesametheotherwayround47BridgeOperation48BridgeDesignAspectsNomodificationtocontentorformatofframeNoencapsulationExactbitwisecopyofframeMinimalbufferingtomeetpeakdemandContainsroutingandaddressintelligenceMustbeabletotellwhichframestopassMaybemorethanonebridgetocrossMayconnectmorethantwoLANsBridgingistransparenttostationsAppearstoallstationsonmultipleLANsasiftheyareononesingleLAN4915.4.2BridgeProtocolArchitectureIEEE802.1DMAClevelStationaddressisatthislevelBridgedoesnotneedLLClayerItisrelayingMACframesCanpassframeoverexternalcommssysteme.g.WANlinkCaptureframeEncapsulateitForwarditacrosslinkRemoveencapsulationandforwardoverLANlink50ConnectionofTwoLANs5115.4.3FixedRoutingComplexlargeLANsneedalternativeroutesLoadbalancingFaulttoleranceBridgemustdecidewhethertoforwardframeBridgemustdecidewhichLANtoforwardframeonRoutingselectedforeachsource-destinationpairofLANsDoneinconfigurationUsuallyleasthoprouteOnlychangedwhentopologychanges52Bridgesand
LANswith
Alternative
Routes
102-105
101-104or107?5315.4.4SpanningTree支撐樹方法BridgeautomaticallydevelopsroutingtableAutomaticallyupdateinresponsetochanges3mechanisms:Frameforwarding幀轉(zhuǎn)發(fā)Addresslearning地址探索Loopresolution環(huán)路消除54FrameforwardingMaintainforwardingdatabaseforeachportListstationaddressesreachedthrougheachportForaframearrivingonportX:SearchforwardingdatabasetoseeifMACaddressislistedforanyportexceptXIfaddressnotfound,forwardtoallportsexceptXIfaddresslistedforportY,checkportYforblockingorforwardingstateBlockingpreventsportfromreceivingortransmittingIfnotblocked,transmitframethroughportY55AddressLearningCanpreloadforwardingdatabaseCanbelearnedWhenframearrivesatportX,ithascomefromtheLANattachedtoportXUsethesourceaddresstoupdateforwardingdatabaseforportXtoincludethataddressTimeroneachentryindatabaseEachtimeframearrives,sourceaddresscheckedagainstforwardingdatabase5615.4.4SpanningTreeAlgorithmAddresslearningworksfortreelayouti.e.noclosedloopsForanyconnectedgraphthereisaspanningtreethatmaintainsconnectivitybutcontainsnoclosedloopsEachbridgeassigneduniqueidentifierExchangebetweenbridgestoestablishspanningtree57LoopofBridges5815.5Layer2andLayer3SwitchesNowmanytypesofdevicesforinterconnectingLANsBeyondbridgesandroutersLayer2switchesLayer3switches5915.5.1Hubs集線器ActivecentralelementofstarlayoutEachstationconnectedtohubbytwolinesTransmitandreceiveHubactsasarepeaterWhensinglestationtransmits,hubrepeatssignalonoutgoinglinetoeachstationLineconsistsoftwounshieldedtwistedpairsLimitedtoabout100mHighdatarateandpoortransmissionqualitiesofUTPOpticalfibermaybeusedMaxabout500mPhysicallystar,logicallybusTransmissionfromanystationreceivedbyallotherstationsIftwostationstransmitatthesametime,collision60HubLayoutsMultiplelevelsofhubscascadedEachhubmayhaveamixtureofstationsandotherhubsattachedtoitfrombelowFitswellwithbuildingwiringpracticesWiringclosetoneachfloorHubcanbeplacedineachoneEachhubservicesstationsonitsfloor61Two-LevelStarTopology62BusesandHubsBusconfigurationAllstationssharecapacityofbus(e.g.10Mbps)OnlyonestationtransmittingatatimeHubusesstarwiringtoattachstationstohubTransmissionfromanystationreceivedbyhubandretransmittedonalloutgoinglinesOnlyonestationcantransmitatatimeTotalcapacityofLANis10MbpsImproveperformancewithlayer2switch63SharedMediumBusandHubsource64SharedMediumHuband
Layer2Switch65Layer2SwitchesCentralhubactsasswitchIncomingframefromparticularstationswitchedtoappropriateoutputlineUnusedlinescanswitchothertrafficMorethanonestationtransmittingatatimeMultiplyingcapacityofLAN66Layer2SwitchBenefitsNochangetoattacheddevicestoconvertbusLANorhubLANtoswitchedLANForEthernetLAN,eachdeviceusesEthernetMACprotocolDevicehasdedicatedcapacityequaltooriginalLANAssumingswitchhassufficientcapacitytokeepupwithalldevicesForexample(Figure15.13)ifswitchcansustainthroughputof20Mbps,eachdeviceappearstohavededicatedcapacityforeitherinputoroutputof10MbpsLayer2switchscaleseasilyAdditionaldevicesattachedtoswitchbyincreasingcapacityoflayer267TypesofLayer2SwitchStore-and-forwardswitchAcceptsframeoninputlineBuffersitbriefly,ThenroutesittoappropriateoutputlineDelaybetweensenderandreceiverBoostsintegrityofnetworkCut-throughswitchTakesadvantageofdestinationaddressappearingatbeginningofframeSwitchbeginsrepeatingframeontooutputlineassoonasitrecognizesdestinationaddressHighestpossiblethroughputRiskofpropagatingbadframesSwitchunabletocheckCRCpriortoretransmission68PreambleSFDDest.
AddressSource
AddressLengthDataFCS6bytes6bytes2bytesMax1500
bytes4bytesCut-through交換機(jī)在收到以太網(wǎng)幀的目的MAC地址之后即開始轉(zhuǎn)發(fā)整個數(shù)據(jù)幀Storeandforward交換機(jī)收到整個數(shù)據(jù)幀后才開始轉(zhuǎn)發(fā)數(shù)據(jù)幀 FrameFrameFrameFrame兩種交換模式69Layer2SwitchvBridgeLayer2switchcanbeviewedasfull-duplexhubCanincorporatelogictofunctionasmultiportbridgeBridgeframehandlingdoneinsoftwareSwitchperformsaddressrecognitionandframeforwardinginhardwareBridgeonlyanalyzesandforwardsoneframeatatimeSwitchhasmultipleparalleldatapathsCanhandlemultipleframesatatimeBridgeusesstore-and-forwardoperationSwitchcanhavecut-throughoperationBridgesufferedcommerciallyNewinstallationstypicallyincludelayer2switcheswithbridgefunctionalityratherthanbridges70ProblemswithLayer2Switches(1)Asnumberofdevicesinbuildinggrows,layer2switchesrevealsomeinadequaciesBroadcastoverload廣播超負(fù)荷Lackofmultiplelinks缺少多鏈路SetofdevicesandLANsconnectedbylayer2switcheshaveflataddressspace單調(diào)地址空間AlluserssharecommonMACbroadcastaddressIfanydeviceissuesbroadcastframe,thatframeisdeliveredtoalldevicesattachedtonetworkconnectedbylayer2switchesand/orbridgesInlargenetwork,broadcastframescancreatebigoverheadMalfunctioningdevicecancreatebroadcaststormNumerousbroadcastframesclognetwork71ProblemswithLayer2Switches(2)CurrentstandardsforbridgeprotocolsdictatenoclosedloopsOnlyonepathbetweenanytwodevicesImpossibleinstandards-basedimplementationtoprovidemultiplepathsthroughmultipleswitchesbetweendevicesLimitsbothperformanceandreliability.Solution:breakupnetworkintosubnetworksconnectedbyroutersMACbroadcastframelimitedtodevicesandswitchescontainedinsinglesubnetworkIP-basedroutersemploysophisticatedroutingalgorithmsAllowuseofmultiplepathsbetweensubnetworksgoingthroughdifferentrouters允許在子網(wǎng)間使用多條路徑72ProblemswithRoutersRoutersdoallIP-levelprocessinginsoftwareHigh-speedLANsandhigh-performancelayer2switchespumpmillionsofpacketspersecondSoftware-basedrouteronlyabletohandlewellunderamillionpacketspersecondSolution:layer3switchesImplementpacket-forwardinglogicofrouterinhardware在硬件上實(shí)現(xiàn)了路由器的分組轉(zhuǎn)發(fā)邏輯TwocategoriesPacketbypacketFlowbased73PacketbyPacketor
FlowBasedOperatesinsamewayastraditionalrouterOrderofmagnitudeincreaseinperformancecomparedtosoftware-basedrouterFlow-basedswitchtriestoenhanceperformancebyidentifyingflowsofIPpacketsSamesourceanddestinationDonebyobservingongoingtrafficorusingaspecialflowlabel流標(biāo)簽inpacketheader(IPv6)Onceflowisidentified,predefinedroutecanbeestablished74TypicalLargeLANOrganizationThousandstotensofthousandsofdevicesDesktopsystemslinks10Mbpsto100MbpsIntolayer2switchWirelessLANconnectivityavailableformobileusersLayer3switchesatlocalnetwork'scoreFormlocalbackboneInterconnectedat1GbpsConnecttolayer2switchesat100Mbpsto1GbpsServersconnectdirectlytolayer2orlayer3switchesat1GbpsLower-costsoftware-basedrouterprovidesWANconnectionCirclesindiagramidentifyseparateLANsubnetworksMACbroadcastframelimitedtoownsubnetwork75TypicalLargeLAN
OrganizationDiagram76AssignmentsRequiredReadingStallingschapter15LoadsofinfoontheW
溫馨提示
- 1. 本站所有資源如無特殊說明,都需要本地電腦安裝OFFICE2007和PDF閱讀器。圖紙軟件為CAD,CAXA,PROE,UG,SolidWorks等.壓縮文件請下載最新的WinRAR軟件解壓。
- 2. 本站的文檔不包含任何第三方提供的附件圖紙等,如果需要附件,請聯(lián)系上傳者。文件的所有權(quán)益歸上傳用戶所有。
- 3. 本站RAR壓縮包中若帶圖紙,網(wǎng)頁內(nèi)容里面會有圖紙預(yù)覽,若沒有圖紙預(yù)覽就沒有圖紙。
- 4. 未經(jīng)權(quán)益所有人同意不得將文件中的內(nèi)容挪作商業(yè)或盈利用途。
- 5. 人人文庫網(wǎng)僅提供信息存儲空間,僅對用戶上傳內(nèi)容的表現(xiàn)方式做保護(hù)處理,對用戶上傳分享的文檔內(nèi)容本身不做任何修改或編輯,并不能對任何下載內(nèi)容負(fù)責(zé)。
- 6. 下載文件中如有侵權(quán)或不適當(dāng)內(nèi)容,請與我們聯(lián)系,我們立即糾正。
- 7. 本站不保證下載資源的準(zhǔn)確性、安全性和完整性, 同時也不承擔(dān)用戶因使用這些下載資源對自己和他人造成任何形式的傷害或損失。
最新文檔
- 合作協(xié)議(五)-合同細(xì)則
- 空調(diào)購銷合作合同書
- 品牌商與供應(yīng)商采購合同范本
- 技術(shù)服務(wù)合同(實(shí)例)
- 詳解:威海房屋過戶合同辦理步驟
- 廢鋼采購及服務(wù)合同全文
- 醫(yī)療事故賠償合同協(xié)議書
- 度證券登記服務(wù)合同協(xié)議
- 雙方黨組織結(jié)對共建合同書
- 建筑試驗(yàn)培訓(xùn)課件
- 智慧環(huán)衛(wèi)項(xiàng)目建設(shè)方案
- 焊接作業(yè)現(xiàn)場環(huán)境溫度濕度記錄
- 長期護(hù)理保險待遇資格申請表
- 馬克思主義基本原理教案:第一章+教案
- 【腳手架計(jì)算書】 腳手架計(jì)算書詳細(xì)步驟
- 工程項(xiàng)目施工過程中的安全分析報告(建設(shè)單位)
- 我的家庭檔案-完整精講版課件
- 機(jī)房電氣系統(tǒng)設(shè)計(jì)方案
- 林木種子質(zhì)量分級
- 白條豬分割測算參考表
- 腹股溝斜疝護(hù)理查房ppt
評論
0/150
提交評論